Complex interactions on fig trees: ants capturing parasitic wasps as possible indirect mutualists of the fig-fig wasp interaction

摘要

Like other mutualisms, pollination mutualisms attract parasites, as well as opportunistic and specialist predators of the pollinators and parasites. These associated species influence the evolutionary dynamics of pairwise mutualisms. Predatory ants are frequent associates of pollination mutualisms, but their effects on the complex interactions between plants, pollinators and parasites have not yet been clearly established, even in the case of the well-described obligate interaction between figs and fig wasps. We attempted to quantify such effects for ants associated with three fig species, two dioecious (Ficus condensa [Brunei], F. carica [France]) and one monoecious (F. racemosa [India]). In all these cases, ant presence on a fig tree strongly reduced the number of parasitic wasps on the figs. Experimental exclusion of ants resulted in an increase in the number of non-pollinating fig wasps on F. condensa and F. racemosa. Experimental ant supplementation led to a decrease in the number of non-pollinating fig wasps on F. carica. Moreover, on F. condensa, the level of reduction of the number of parasitic wasps depended on the number and identity of the ants. On F. carica, non-pollinating fig wasps even avoided trees occupied by the dominant predatory ant. The consistency of the effect of ants in these three cases, representing a geographically, ecologically, and taxonomically broad sample of figs, argues for the generality of the effect we observed. Because reduction of parasitism benefits the pollinator, ants may be considered as indirect mutualists of plants and pollinators in the network of complex interactions supported by fig trees.